Studies　on　the　effect　of　near-surface　overburden　soil　layers　on　seismic　motion　have　shown　that　the　overburden　soil　layers　have　a　significant　impact　on　the　seismic　effect　of　the　site　due　to　the　formation　age,　genetic　type,　thickness　difference,　structure,　and　dynamic　characteristics　of　the　soil　layers.　In　this　paper,　the　one-dimensional　seismic　response　analysis　of　a　nuclear　power　plant　site　containing　a　thick　hard　interlayer　was　conducted　to　discuss　the　influence　of　the　hard　interlayer　thickness　on　the　site　seismic　response,　so　as　to　provide　a　basis　for　determining　the　seismic　motion　parameters　for　seismic　design　of　similar　sites.　Based　on　the　engineering　geological　data　of　a　nuclear　power　plant　site,　five　models　of　one-dimensional　soil-layer　seismic　response　analysis　were　built,　and　the　equivalent　linear　method　of　the　one-dimensional　site　seismic　response　was　applied　to　analyze　the　effect　of　the　interlayer　thickness　on　the　peak　acceleration　and　the　acceleration　response　spectra　of　the　site　seismic　response.　The　seismic　response　characteristics　of　the　site　and　influence　rules　of　the　hard　interlayer　thickness　are　summarized　as　follows:　1)Under　different　input　seismic　motion　levels,　the　peak　acceleration　at　the　top　of　the　hard　interlayer　was　less　than　the　input　peak　acceleration,　and　the　peak　acceleration　at　the　ground　surface　of　site　was　greater　than　the　input　peak　acceleration.　2)Under　the　same　input　seismic　motion,　the　ratios　of　the　peak　accelerations　at　the　top　of　hard　interlayer　to　the　input　peak　accelerations　were　smaller　than　the　ratios　of　the　peak　accelerations　at　the　ground　surface　to　the　input　peak　acceleration,　and　these　ratios　first　decreased　and　then　increased　gradually　with　the　increase　of　the　hard　interlayer　thickness;　while　for　the　same　hard　interlayer　thickness,　these　ratios　gradually　decreased　as　the　input　peak　acceleration　increasing.　3)For　the　same　input　seismic　motion,　the　ratios　of　the　peak　accelerations　at　the　ground　surface　of　site　to　those　at　the　top　of　the　hard　interlayer　increased　gradually　as　the　hard　interlayer　thickness　increased;　however,　corresponding　to　different　hard　interlayer　thicknesses,　the　variation　characteristics　of　ratios　which　are　the　peak　accelerations　at　the　ground　surface　of　site　to　those　at　the　top　of　the　hard　interlayer　were　inconsistent　with　the　increase　of　the　input　peak　acceleration.　4)The　hard　interlayer　had　a　significant　influence　on　the　short-period　acceleration　response　spectrum　and　the　thicker　the　hard　interlayer　was,　the　wider　the　influence　frequency　band　would　be;　while　for　a　special　hard　interlayer　thickness,　the　influence　frequency　band　is　certain,　and　the　hard　interlayer　had　little　effect　on　the　acceleration　response　spectrum　coordinates　outside　this　frequency　band,　the　longer　the　period　is,　the　less　the　influence　of　the　hard　interlayer　on　the　acceleration　response　spectrum　coordinates.　The　seismic　response　characteristics　of　the　site　and　influence　rules　of　the　hard　interlayer　thickness　indicate　that　the　hard　interlayer　thickness　has　a　significant　impact　on　the　peak　acceleration　and　the　acceleration　response　spectra　of　the　site　seismic　response,　and　the　hard　interlayer　has　obvious　isolation　effect　at　the　seismic　motion,　and　the　increase　of　its　thickness　reduces　the　nonlinear　effect　of　the　site　and　leads　to　the　wider　influence　frequency　band.　Meanwhile,　the　higher　the　input　peak　acceleration　is,　the　stronger　the　nonlinear　effect　of　the　site,　and　it＇s　remarkable　that　the　soft　layer　overlying　the　hard　interlayer　has　a　significant　amplification　effect　on　the　seismic　motion.　©　2019,　Editorial　Office　of　Seismology　and　Geology.　All　right　reserved.